The present invention relates generally to a method and system for updating a customer telephone number list based on latest status information, and more particularly to a method and system for examining the utilization of telephone numbers by calling a telephone number on a normal analog telephone line from an ISDN (Integrated Services Digital Network) line in a digital communication mode, determining the current status of the telephone line from information obtained from such a call, and updating the telephone number list.
An example of the prior art technique for updating a telephone number list is disclosed in Japanese Laid-Open Patent Application No. 17-177214. The system disclosed in the application sequentially reads out telephone numbers from a customer telephone number list stored in a storing device, sends each telephone number to an analog public telephone network through an analog telephone line, and determines whether the called telephone number is valid or invalid from a reaction made in response to the sending of the telephone number, thereby automatically updating the telephone number list.
When a telephone number is sent to an ordinary telephone line, i.e., an analog line, the system mainly receives (1) a call back tone signal indicating that a called party is being called; (2) a busy tone signal indicating that the called party is speaking; (3) a polarity inverted signal indicating that the called party has responded to the call; or (4) a recorded audio message indicating that the called telephone number is not in use or has been changed.
The system disclosed in the aforementioned prior art determines that a telephone number is valid if a call back tone signal or a polarity inverted signal is detected within a predetermined time period after a call is made. Also, when an audio message is received, the contents of the message are recognized by an operator or is automatically perceived by a speech recognition apparatus.
Thus, the prior art system requires a sufficient waiting time for receiving a response signal from a station which attends to a calling operation.
Also, the response signal from the station attending to the calling operation may be a polarity inverted signal, a call back tone signal, a busy tone signal, or an audio message. Thus, the response signal takes a variety of signal forms, so that complicated signal detection processing is required.
Further, for perceiving the contents of an audio message, an additional time is required for recognizing the contents of the message irrespective of whether an operator intervenes or an automatic speech recognition apparatus is used.